The present invention relates to a primer composition or, more particularly, to a primer composition and a method for improving the adhesive bonding between a condensation-type room temperature-curable silicone rubber composition and the surface of a substrate such as a paint-coated metal body.
It is conventional in the modern building works that the outer walls of a building are finished by using various kinds of metallic materials coated on the surface with a paint or coating composition containing fluorocarbon resins, urethane resins, acrylic resins and the like as the vehicle in order to be imparted with improved weatherability, attractive appearance and other desirable properties. It is also conventional in the building works that a room temperature-curable silicone rubber composition of the condensation-curable type is used as a sealing material for impregnating and preventing water leakage through joints and interstices formed in the outer walls of a building constructed by using paint-coated metallic materials.
It is essential in the above mentioned application of a room temperature-curable silicone rubber composition that strong adhesive bonding is obtained between the cured silicone rubber and the paint-coated surface of the wall materials while this is not always an easy matter so that troubles of water leakage are some-times caused at the joints due to incomplete adhesive bonding between the sealing material and the paint-coated surface. This problem of incomplete adhesive bonding can be at least partly solved by the pre-treatment of the paint-coated substrate surface with a primer composition prior to contacting with the room temperature-curable silicone rubber composition. Various types of primer compositions have been proposed and are used for the purpose, of which those containing a hydrolyzable organosilane compound or a hydrolysis-condensation product thereof as the principal ingredient are widely used. None of these prior art primer compositions, however, can be satisfactory due to the incompleteness of the priming effect obtained therewith.